I have a head cannon that goes with this one, but it's currently nearly three in the freaking morning and I don't want to type it out.

Short version is; Twilight is 'helping' Shining Armor with his cadet helm by skedaddling off with the thing to polish it for drills, but failed to communicate that with her big brother. A vaudeville-esque chase through the castle ensues.

Celestia is amused. The bourgeois are decidedly not.

Cadance helps. Sort of.

No, I didn't forget Twilight's cutie mark, she's very young here.